1. Field of the Invention
This invention relates to a lens mechanism, more particularly, to an improved zoom lens mechanism which can be readily assembled or disassembled. This zoom lens mechanism is specially suitable for LCD Projector System.
2. Description of the Prior Art
The zoom lens used on the commercial LCD Projector System can be classified into two categories, the standard lens and zoom lens. When the LCD Projector System is only incorporated with a standard lens, the projecting system shall be moved to a desired position to enlarge the screen, accordingly, a better effect can be reached.
When the LCD Projector System is equipped with a zoom lens, the user can select a suitable size of screen according to the environment. This projecting system equipped with zoom lens are specially suitable for the room is not robust. By virtue of this zoom lens, the projecting system can be fixed to a predetermined position to get a best effect.
Normally, the zoom lens includes a first and a second group of lens. According to the optical design of said lens, the diameter of first group of lens is larger than the diameter of second group of lens. Besides, the focus is based on the first group of lens. As shown in FIG. 1, a conventional configuration of a zoom lens which is disclosed in U.S. Pat. No. 5,144,494. According to its design, a first housing 18 is directly attached to the first group of lens 19 and the first housing 18 is screwed to the focusing ring 56. Besides, the end portion of said focusing ring 56 is screwed to lens barrel 57. As a result, the outer diameter as well as the length of said lens is inevitable increased.
The second and third housings 28, 38 are moved by the adjusting ring 58, ring gear 59 and cam ring 68. This axial movement of said adjusting ring 58 is anchored and transmitted to the barrel 67 which is interconnected with the second and third housings 28, 38. On the other hand, the cam ring 66 can be also adjusted by the manipulating ring 68 via the pin 67. This conventional lens has a very complicated configuration.
On the other hand, in adjusting the rear focus, a cam 77 is utilized to change the relative position of the adjusting ring 58 and the inner fixed barrel 67. Because the cam 77 has only an actuating point, it is difficult to adjust the rear focus, on the country, the relative position between said cam 77 and said inner fixed barrel 67 tends to shift tiltedly. Besides, during the adjustment, the cam ring 66 is moved directly up and down, accordingly, all the group lens are moved. In light of this, this need a more larger force in adjusting the group lens. No doubt this will bring an inconvenience to the user. An improvement is apparently necessary.